One-Step, High-Yield Deconstruction of Kraft Lignin Into a Redox-Active Small Molecule Using Sonicated Emulsive Water Microdroplets.

Lignin is an abundant biofeedstock that holds great potential for producing renewable organic chemicals, but its effective valorization is difficult due to low conversion rates and the need for harsh reaction conditions, which impact selectivity. Here, we introduce an alternative to catalyzed thermochemical and electrochemical methods consisting of a fast one-step (∼20 min) uncatalyzed use of sonicated emulsive water microdroplets (SEWMs) to efficiently deconstruct Kraft lignin (∼14.2 kDa). We converted Kraft lignin selectively and in high yield ( ∼ 56% ± 5%) into SEMILL-A (∼656 Da), composed of possible structural isomers of a redox-active small molecule to which we assigned a structure consisting of substituted nitrophenyl units attached to a coumarin dicarboxylic acid core. Characterization of SEMILL-A was carried out using infrared spectroscopy, 1D and 2D nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry, chromatography, and electrochemical analysis. We show the possibility of SEWMs to activate C─C bond cleavage and to facilitate reductive nitration in Kraft lignin and a model compound. Our study highlights a distinctive reactive environment within SEWMs where sonochemical excitation and redox microdroplet chemistry synergistically enable novel deconstructive pathways for biofeedstock valorization.